There is an ever increasing need to identify and map the locations of source materials, such as radiation emitting areas, mineral or oil deposits, hazardous or toxic wastes, or the like, on various sites. It is often important to quantitatively and/or qualitatively identify the source materials. Because most sites are not flat, it has not been possible, heretofore, to satisfactorily traverse the sites in a planned scanning or other mapping series of traverses in order to sufficiently mark and map the source material or radiation emitting areas on the site.
Aerial survey, sometimes used for identifying source materials, is disclosed in U.S. Pat. No. 3,825,751, entitled Method and Apparatus for Aerial Radioactivity Surveying for Surface Mineral Deposits Which Compensates for the Radioactive Decay Products in the Atmosphere of the Earth, to Johnson, et al; U.S. Pat. No. 2,557,158, entitled Radioactive Exploration, to Teichmann; U.S. Pat. No. 4,421,981, entitled Method and Apparatus for Conducting Remote Surveys of the Earth's Crust, to Hough; and U.S. Pat. No. 4,581,531, entitled Method for Identifying Hydrothermal Alteration Areas of the Earth, to Dion. However, to obtain more accurate surveys than provided by these devices, the detectors must be fairly close to the ground.
To locate, mark, quantify, and map radiologically active areas, some of which are not very radioactive or "hot," one must use detectors positioned a few inches above the ground. Because of the irregularities in most terrain, it has been nearly impossible to traverse terrain in an accurate scanning movement by vehicle. Many sites are several square miles in size and to survey them on foot is an expensive and time consuming task. Moreover, survey by foot is difficult because personnel find it difficult to follow a predetermined traversing pattern accurately and to maintain optimum detector height. Furthermore, survey by foot may expose personnel to radionuclides.
Land vehicle mounted survey or prospecting devices are disclosed in the following patents. U.S. Pat. No. 2,562,914, entitled Prospecting, to Herzog, discloses detectors which are mounted on the top of a vehicle. U.S. Pat. No. 3,008,046, entitled Method of and Apparatus for Making a Geophysical and Topographical Map, to Carpenter, discloses a combination odograph, scintillation counter-recorder, and an altimeter-recorder, connected to the wheel of a vehicle.
U.S. Pat. No. 3,124,684, entitled Plutonium Detector, to Eberline, discloses a plutonium detector which is a single unit attached to the front bumper of a vehicle. U.S. Pat. No. 3,341,706, entitled Apparatus for and Method of Terrestrial Surveying, to Swift et al, and U.S. Pat. No. 3,354,310, entitled Mobile Density and Moisture Content Sensing Device for Continuous Logging of a Terrestrial Surface, to Swift, disclose a detector which is pulled on a trailer behind a vehicle. U.S. Pat. No. 4,317,033, entitled Gamma Ray Prospecting System, to Penenka, et al, discloses a gamma ray prospecting system. None of these patents disclose a plurality of independently positionable detectors which follow the terrain as the vehicle moves across the terrain.
Another prior art land vehicle mounted radiation survey device is manufactured by Rockwell International in Richland, Washington, for the Hanford Site. This device, called the "Mobile Surface Contamination Monitor (MSCM)," is a tractor-driven unit with five sodium iodide (NaI) crystal detectors mounted on a rigid horizontal tool bar at the front of the tractor. A sixth (background) detector is mounted at the rear of the tractor on a rear tool bar. Each of the five active detectors is enclosed in a side collimated assembly that limits its field-of-view and does not adequately cover the space between the detectors. Because the detectors are mounted rigidly on a horizontal bar, the detectors are not maintainable at a preselected height above the ground as the tractor moves over the ground because the ground terrain is almost never flat. Thus, the detectors cannot be accurately utilized. The MSCM can only be used for traversing very flat, consistent terrain. In fact, when the tractor tilts, the detectors often hit the ground and can be damaged. If the detectors are to be raised, the entire horizontal bar is raised, thus raising all of the detectors at once. In addition, the MSCM does not automatically mark the "hot" spots. An operator must stop the vehicle, get out of the cab, and physically place flags at the place of contamination. This requires excessive time, results in low marking accuracy, and potentially exposes the operator to radioactivity. Furthermore, the MSCM does not differentiate between one or more radionuclides; it merely detects that gamma or beta radiation is present. The MSCM does not provide for mapping of the survey site. This makes follow-up work, such as radiation clean-up, difficult and inaccurate.
The following patents disclose tractors or other heavy equipment which are used for agricultural purposes, and which provide independent movement of implements. U.S. Pat. No. 2,395,322, entitled Tractor Mounted Implement, to Evans, discloses bars positioned on the back of the tractor, to which two plows are connected. The bars allow the plows to move up and down, independently, when controlled by the farmer. U.S. Pat. No. 2,800,847, entitled Selective Control Mechanism for Tractors, to Bennett; U.S. Pat. No. 3,433,310, entitled Ripper Tooth Mounting for Earth-Working Machines, to Harper; and U.S. Pat. No. 4,248,310, entitled Skip Row Cultivators, to McWilliams, teach hydraulically assisted independent movement of implements attached to a horizontal bar on a tractor, a bulldozer, or the like, by operator control. As stated above, movement of the implements is operator controlled and not automatic, based on the terrain. None of these devices is suitable for carrying a detector device above the ground, nor would any of the above devices allow automatic following by a detector device of somewhat irregular terrain.
The following patents utilize various means for providing location of a mobile receiver. U.S. Pat. No. 3,715,758, entitled Methods and Apparatus for Precise Positioning of Locations, to Sender; and U.S. Pat. No. 4,232,317, entitled Quantized Hyperbolic and Inverse Hyperbolic Object Location System, to Freeny, disclose radio location systems. U.S. Pat. No. 3,918,056, entitled Radar Trilateralization Position Locators, to Merrick; and U.S. Pat. No. 3,938,146, entitled Secure Encoder for Trilateralization Locator Utilizing Very Narrow Acceptance Periods, to Dano, both teach radar location systems. Worth, et al, in "Use of a Commercial Ranging System in Field Surveys of Radioactively Contaminated Sites," presented at IEEE Nuclear Science Symposium (1984), discloses the use of a microwave ranging system.